a) Field of the Invention
The present invention is directed to a device for the implantation of pellets containing medication in animals, which device has a housing in the shape of a pistol with a handle, a hollow needle for injecting the body of the animal being arranged at the front side of the housing, and a push rod. The push rod can be slid into this hollow needle and is supported in the housing so as to be displaceable longitudinally. A shaft is provided in the housing prior to the needle for a magazine holding pellets which is displaceable therein. A longitudinally displaceable press-back device is arranged in the housing parallel to the push rod and hollow needle. The push rod and press-back device are moved by a driving mechanism which is similarly provided in the housing and which can be set in motion by an operating lever fastened at the handle via a toothed segment coupled with the operating lever and a toothed wheel engaging with the latter.
b) Description of the Related Art
In a device of this kind known from U.S. Pat. No. 4,447,223, the driving mechanism between the toothed segment and toothed wheel on one side and the push rod on the other side is formed by a gear unit which is connected between the latter and substantially includes an additional toothed wheel and a horizontal toothed rack of determined length which, in addition to moving the push rod through the pellet magazine and into the hollow needle, also drives the press-back device and advances the pellet magazine at the same time.
This driving mechanism works very directly, i.e. there is no play in the transmission of force between the toothed wheels and the toothed rack, and since the push rod is securely connected with the toothed rack, the latter can not move relatively to one another. Therefore, teeth can be broken off the toothed rack when the driving mechanism is overloaded, in particular when the device is soiled to some extent in this region.
It has already been suggested in DE-OS 41 06 196 to use a strip-shaped member as a driving mechanism for driving the push rod so that force may be transmitted from the operating lever to the push rod without the intermediary of a toothed rack and a toothed wheel engaging in the latter.
The strip-shaped member is a flat, resilient metal strip which is guided by its edges in two opposite U-shaped profiles or sections. One end of this strip is fastened to a wind-up drum which is driven by a toothed segment provided at the operating lever and by a toothed wheel which engages with the latter and is connected coaxially with the wind-up drum. The other end of the metal strip is fastened to the push rod. By moving the operating lever at the handle of the pistol-shaped implanting device, the wind-up drum rotates and winds up the metal strip so that the end fastened to the push rod is drawn forward and the push rod moves into the pellet magazine provided in the front part of the implanting device so that a pellet is pushed out of the latter and into the hollow needle and is pushed through the latter and implanted in the cavity formed in the body of the animal by the hollow needle.
The return movement of the push rod is not brought about by the metal strip, but rather by a spiral spring arranged on the push rod which is compressed when the push rod is drawn forward and presses the latter back into its initial position at the end of the implantation process. In so doing, the push rod draws the metal strip off the wind-up drum again so that the operating lever is also moved back into its initial position. This driving mechanism is relatively complicated and is therefore subject to frequent problems, particularly in that the metal strip guided in the U-shaped sections jams easily as the implanting device becomes dirty so as to impair the operating reliability of the device.